Broadband Plasma Processing Systems and Methods

ABSTRACT

An exemplary plasma processing system includes a plasma processing chamber, an electrode for powering plasma in the plasma processing chamber, a tunable radio frequency (RF) signal generator configured to output a first signal at a first frequency and a second signal at a second frequency. The second frequency is at least 1.1 times the first frequency. The system includes a broadband power amplifier coupled to the tunable RF signal generator, the first frequency and the second frequency being within an operating frequency range of the broadband power amplifier. The output of the broadband power amplifier is coupled to the electrode. The broadband power amplifier is configured to supply, at the output, first power at the first frequency and second power at the second frequency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 16/572,708, filed on Sep. 17, 2019, which application is herebyincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates generally to plasma systems and methods ofoperation, and, in particular embodiments, to broadband plasmaprocessing systems and methods.

BACKGROUND

Generally, semiconductor devices, such as integrated circuits (ICs) arefabricated by sequentially depositing and patterning layers ofdielectric, conductive, and semiconductor materials over a semiconductorsubstrate using photolithography and etch to form structures for circuitcomponents and interconnect elements (e.g., transistors, resistors,capacitors, metal lines, contacts, and vias). Some components compriseintricate three-dimensional structures, for example, stack-capacitors indynamic random access memory (DRAM) cells and fin field-effecttransistors (FinFETs). Plasma-assisted techniques such as reactive ionetching (RIE), plasma-enhanced chemical vapor deposition (PECVD),plasma-enhanced atomic layer etch and deposition (PEALE and PEALD) havebecome indispensable in the deposition and etching processes used toform the semiconductor device structures.

The minimum feature sizes are periodically reduced to reduce cost byincreasing packing density. Features of a few nanometers can bepatterned with innovations such as immersion lithography and multiplepatterning. This scaling trend intensifies the technological challengein forming dense, high aspect ratio nanostructures. In particular,plasma processes provide the capability of forming nanostructures ofaccurate dimensions along with precisely controlled structural features(e.g., width, depth, edge profile, film thickness, conformality, andanisotropy), often at atomic scale dimensions, uniformly across a wide(e.g., 300 mm) wafer. A variety of plasma processing techniques such asselective deposition and etch, concurrent deposition and etch, pulsedplasma processes, and cyclic processes using alternating deposition andetch cycles have been developed to overcome some of the hurdles infabricating scaled semiconductor devices. Successful deployment of suchtechniques in semiconductor manufacturing may need further innovationsin plasma equipment design that consider factors such as processingcost, equipment configurability, and equipment cost.

SUMMARY

In accordance with an embodiment of the present invention, a plasmaprocessing system includes a plasma processing chamber, a firstelectrode for powering a plasma in the plasma processing chamber, atunable radio frequency (RF) signal generator configured to output afirst signal at a first frequency and a second signal at a secondfrequency. The second frequency is at least 1.1 times the firstfrequency. The system further includes a broadband power amplifiercoupled to the tunable RF signal generator, the first frequency and thesecond frequency being within an operating frequency range of thebroadband power amplifier. The output of the broadband power amplifieris coupled to the first electrode. The broadband power amplifier isconfigured to supply, at the output, first power at the first frequencyand second power at the second frequency.

In accordance with an embodiment of the present invention, a plasmaprocessing system includes a tunable radio frequency (RF) signalgenerator configured to output a first signal at a first frequency and asecond signal at a second frequency. The second frequency is at least1.1 times the first frequency. The system further includes a broadbandpower amplifier coupled to the tunable RF signal generator. The firstfrequency and the second frequency is within an operating frequencyrange of the broadband power amplifier. The output of the broadbandpower amplifier is configured to be coupled to an electrode of a plasmaprocessing chamber. The broadband power amplifier is configured tosupply, at the output, first power at the first frequency and secondpower at the second frequency, and provide a feedback to tune the outputof the broadband power amplifier to the first frequency or the secondfrequency.

In accordance with an embodiment of the present invention, a method ofoperating a plasma processing system comprises generating a radiofrequency (RF) signal at tunable RF signal generator; at a broadbandpower amplifier, amplifying the RF signal to generate an amplified RFsignal; supplying the amplified RF signal to power a plasma within aplasma processing chamber; generating a feedback signal by measuring animpedance of the plasma; and adjusting a frequency of the RF signal atthe tunable RF signal generator based on the feedback signal.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic of a broadband plasma system comprising a plasmaprocessing apparatus illustrated in a cross-sectional view in accordancewith an embodiment of the invention;

FIG. 2 is a schematic of a single channel broadband RF power amplifierin accordance with an embodiment of the invention;

FIG. 3 is a schematic of a broadband plasma system comprising a plasmaprocessing apparatus illustrated in a cross-sectional view in accordancewith an alternative embodiment of the invention;

FIG. 4 is a schematic of a broadband plasma system comprising a plasmaprocessing apparatus illustrated in a cross-sectional view in accordancewith an alternative embodiment of the invention;

FIG. 5 is a schematic of a broadband plasma system comprising a plasmaprocessing apparatus illustrated in a cross-sectional view in accordancewith an alternative embodiment of the invention;

FIG. 6 is a schematic of a dual channel broadband RF power amplifier inaccordance with an alternative embodiment of the invention;

FIG. 7 is a schematic of a broadband plasma system comprising a plasmaprocessing apparatus illustrated in a cross-sectional view in accordancewith an embodiment of the invention;

FIG. 8 is a schematic of a broadband plasma system comprising a plasmaprocessing apparatus illustrated in a cross-sectional view in accordancewith an alternative embodiment of the invention;

FIG. 9 is a schematic of a broadband plasma system comprising a plasmaprocessing apparatus illustrated in a cross-sectional view in accordancewith an alternative embodiment of the invention; and

FIG. 10 discloses a method of operating a plasma processing system inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In conventional plasma processing, etching tools and deposition toolshave separate processing chambers. However, many process recipes requirerepeated etching and deposition, which can take a significant amount ofprocessing time as the wafer has to be transferred without breakingvacuum between the different chambers. Combining deposition and etchprocesses in a single chamber can reduce processing time when suchmultiple deposition and etching processes are being performed. Forexample, a single chamber that can do a variety of etch and depositionprocesses can help to eliminate wafer transfer between different etchand deposition chambers. Different plasma deposition and etch processes(e.g., isotropic and directional deposition/etch) may operate at widelydifferent radio frequencies and hence use very different hardwareespecially having different RF sources and matching networks. Thedifferent RF source also would have separate RF isolation, making thesystem more complex. Further complexity may occur if, for example, theplasma processing apparatus comprises a first RF electrode connected toan RF signal having a first RF frequency, and a second RF electrodeconcurrently connected to an RF signal having a second RF frequency. Inaddition, traditionally, tuning several separate matching networks isvery time-consuming. Not only would the tuning be done at each operatingfrequency but also the tuning is a slow mechanically driven procedure.

Embodiments of the present application disclose a single-chamber design,e.g., for doing both etching and deposition processes. Embodiments ofthe present application disclose a broadband power amplifier coupledwith an electronic feedback control system that helps to quickly togglebetween etch and deposition processes. The electronic feedback controlsystem is designed to tune a broadband RF signal generator for ultrafastimpedance matching.

An embodiment of a broadband plasma system utilizing a single channelbroadband RF power amplifier is first described using FIG. 1. The singlechannel broadband RF power amplifier is then described in further detailwith reference to FIG. 2. Other example embodiments of broadband plasmasystems utilizing the single channel broadband power amplifier aredescribed with reference to FIGS. 3 and 4. A broadband plasma system,wherein the plasma processing chamber may be operated in adual-frequency mode using a dual channel broadband RF power amplifier isdescribed using FIG. 5. The dual channel broadband RF power amplifier isthen described in further detail with reference to FIG. 6. Embodimentsillustrating pulsed mode operation using broadband plasma systemscomprising an electronically controlled pulse generator are describedwith reference to FIGS. 7-9. An exemplary method of operating a plasmaprocessing system will then be discussed in FIG. 10.

FIG. 1 illustrates a schematic representation of a broadband plasmaprocessing system 1111 comprising a plasma processing apparatus 111which includes, for example, a plasma processing chamber 150 illustratedin a cross-sectional view.

In one embodiment, the plasma processing chamber 150 is fitted with afirst RF electrode 156 near the top and a substrate holder 158 near thebottom inside the chamber, as illustrated in FIG. 1. The first RFelectrode 156 and the substrate holder 158 may be circular in oneembodiment. During a plasma processing step, a substrate (e.g., asemiconductor wafer) may be placed on the substrate holder 158. Thesubstrate temperature may be adjusted by a feedback temperature controlsystem 154 using heaters and coolers in the substrate holder 158 tomaintain a specified temperature.

A programmable controller 110 may be programmed with a process recipe120, e.g., stored in a memory of the broadband plasma processing system1111 as programmable instructions. The process recipe 120 provides theinformation used to select a center frequency of a narrow band of thebroadband tunable RF signal generator 100. Generally, the RF signalgenerator 100 generates a sinusoidal waveform. In some embodiments,other waveforms may be generated, for example, a sawtooth waveform.Based on the process recipe 120, the programmable controller 110generates a first control signal that is then transmitted to a tunableRF signal generator 100. During processing, the programmable controller110 may refine the RF frequency with a small frequency offset within theselected narrow operating frequency band, as explained further below.

During operation, the plasma process is driven by RF power and DC biassupplied to one or more electrodes of the plasma processing chamber. Theoperation mode of the plasma processing chamber may be altered by aprogrammable controller with control signals controlling the frequencyand magnitude of the RF power and DC bias applied at each electrode.

Based on the first control signal, the tunable RF signal generator 100generates an RF signal that is provided at an input port I of abroadband RF power amplifier 1000. The broadband RF power amplifier 1000outputs an amplified RF signal at its output port O, which is thenprovided to power the plasma, e.g., through the first RF electrode 156.The broadband RF power amplifier 1000 has an operating frequency rangebetween at least 0.1 MHz and 10 GHz. In one exemplary design of thebroadband RF power amplifier 1000 an operating frequency range between400 kHz to 3 GHz is used.

In the example embodiment illustrated in FIG. 1, a direct plasma may besustained between the substrate and the first RF electrode 156 using RFpower coupled to the plasma from the first RF electrode 156 and agrounded substrate. In one embodiment, the grounded substrate comprisesconnecting the substrate holder 158 to a reference potential, referredto as ground.

The process recipe 120 is also used by the programmable controller 110to send a second control signal to a signal port S of the broadband RFpower amplifier 1000, where the second control signal is used toconfigure internal switches (e.g., solid-state electronic switches suchas thyristors and insulated-gate bipolar transistors (IGBTs)) thatselect an output matching network in the broadband RF power amplifier1000. The selected output matching network corresponds to the centerfrequency of the narrow operating frequency band selected using theinitial first control signal, thereby ensuring that the components ofthe output matching network are aligned with the operating frequencyband, as specified by the process recipe 120.

A feedback signal from a feedback port Z of the broadband RF poweramplifier 1000 to the programmable controller 110 fine tunes the outputfrequency at the output port O of the broadband RF power amplifier 1000.The feedback signal is a measure of the efficiency with which RF poweris transferred from the broadband RF power amplifier 1000 to the plasmaand may be used by the programmable controller no to fine tune thefrequency of the RF signal by adjusting the first control signal to theRF signal generator to dynamically tune the RF signal frequency, forexample, to maintain maximum power transfer efficiency. The powertransfer efficiency is indicated by the fraction of power reflected atthe output port O. Accordingly, in one embodiment, the forward power andreflected power is measured and a feedback signal proportional to thereflected power is generated using circuitry internal to the broadbandRF power amplifier 1000, as explained in further detail below withreference to FIG. 2.

Still referring to FIG. 1, the plasma processing chamber 150 comprises atubular sidewall 101, a base 105, and a top cover 103 that collectivelysubstantially enclose the plasma processing chamber 150. The sidewall101, base 105, and top cover 103 may be made of a conductive materialsuch as stainless steel or aluminum coated with a film such as yttria(e.g., Y_(x)O_(y) or Y_(x)O_(y)F_(z)), or a film consistent with theprocess (e.g., carbon or silicon), or as known to a person skilled inthe art. Generally, the plasma processing chamber 150 is connected toground although, in some embodiments, the plasma processing chamber 150may be floating.

In the example embodiments in this disclosure, carrier and process gasesare introduced into the plasma processing chamber 150 by a gas inputsystem comprising inlets 155 in the sidewalls 101. The gas input systemmay include multiple inlets and may input different gases into theplasma processing chamber 150 at different times, as specified in theprocess recipe. For example, the design may include additional gasinlets through the top cover 103. A gas exhaust system comprising, forexample, outlets 107 in the base 105 and vacuum pumps 152 may be used toremove exhaust gases such as product gases from the plasma processingchamber 150. The vacuum pumps 152 maintain a gas flow between the inlets155 and outlets 107 of the plasma processing chamber 150.

Various other components of the input and exhaust systems (e.g., flowmeters, pressure sensors, and control valves), plasma parameter sensors(e.g., optical emission spectroscopy (OES) sensor, a quadrupole massspectrometer (QMS), and Langmuir probe), electrostatic grids, electricalconnectors, etc. inside the plasma processing chamber 150 are not shownand would be known to a person skilled in the art.

The design of the first RF electrode 156 (e.g., its diameter, thickness,resistance, and self-inductance), the design of the substrate holder(e.g., its diameter, pedestal height, geometry of the built-in heatingand cooling elements would be known to a person skilled in the art andtherefore not discussed further.

Although components of the plasma processing apparatus 11 illustrated inFIG. 1 have specific geometrical shapes and placements, it is understoodthat these shapes and placements are for illustrative purposes only;other embodiments may have other shapes and/or placements.

In the broadband plasma processing system 1111 illustrated in FIG. 1, RFpower from the broadband RF power amplifier 1000 is transferred to adirect plasma using the first RF electrode 156, disposed within theplasma processing chamber 150.

In further embodiments, the first RF electrode 156 may be placed outsidethe plasma processing chamber 150 and coupled inductively/capacitivelyto the plasma within the plasma processing chamber 150. In some otherembodiments, the first RF electrode 156 may be replaced with a planarspiral coil disposed over the top cover 103, wherein a portion of thetop cover 103 below the planar coil comprises a dielectric window. Inyet other embodiments, a helical coil wrapped around the outer surfaceof the tubular sidewall 101 may be used, wherein the sidewall 101comprises a dielectric material. In some embodiments, the plasma insidethe plasma processing chamber 150 may be sustained by a microwave powersource (e.g., a magnetron or solid state microwave generator) using aslotted antenna such as an annular waveguide located outside the tubularsidewall 101 or a slotted antenna disk disposed over the top cover 103.The microwave power from the annular waveguide may be coupled to theplasma using dielectric cover along the annular waveguide and thesidewall 101, and the microwave power from the slotted antenna disk maybe coupled to the plasma using a portion of the top cover 103 below theslotted antenna disk as a dielectric window.

Also, in further embodiments, a remote plasma (as opposed to a directplasma) may be used to process the substrate by using a chamber designwherein the plasma discharge is located remote from the substrateholder.

Next we refer to the schematic view in FIG. 2 to describe a construct ofthe single channel broadband RF power amplifier 1000 having four ports:input port I, output port O, signal port S, and feedback port Z,connected to various other circuits of the broadband plasma system asdescribed above with reference to FIG. 1.

As illustrated in FIG. 2, an input signal at some RF frequency appliedto input port I is distributed to an array of power amplifiers 220powered by DC power supplies 210 indicated by the wide arrow drawnacross the amplifier array. Collectively, the array of power amplifiers220 span a wide range of frequency, although any one of the eight poweramplifiers 220 in FIG. 2 may be designed to amplify an RF signal withina relatively narrow frequency band. The power amplifiers 220 maycomprise laterally-diffused or extended-drain metal-oxide-semiconductor(LDMOS or EDMOS) silicon transistors, or silicon carbide, or galliumnitride based power devices, or the like, depending on power andfrequency.

The outputs from the power amplifiers 220 are combined by a set ofcombiners in one or more stages, for example, the set of two four-inputintermediate combiners 230 and one two-input final combiner 240.Collectively, the array of power amplifiers 220, the four-inputintermediate combiners 230 and the final combiner 240 function as abroadband power amplifier unit. As is known to a person skilled in theart, the number of amplifiers and combiners may be chosen based on theindividual design requirements of the plasma system.

The output of the final combiner 240 is connected to an electronicallyconfigurable network of passive elements, referred to as an outputmatching network, comprising, for example, a tuning capacitor (C_(T)), aload capacitor (C_(L)), and an optional inductor (L). As known to aperson skilled in the art, the impedance of an output matching networkcomprising capacitors (or inductors) is frequency-dependent. Since thebroadband plasma system 1111 may be operating the plasma processingapparatus 11 at widely spaced frequency bands, the capacitance (orinductance) value used has to be aligned with the operating frequencyspecified in the process recipe 120. Accordingly, whenever the processrecipe 120 specifies a different operating RF frequency, theprogrammable controller 110 may generate a new second control signal forthe broadband RF power amplifier 1000 to select one or more componentsfrom multiple passive components in an output matching network circuit250.

In one embodiment, the output matching network circuit 250 uses thesecond control signal received at the signal port S of the broadband RFpower amplifier 1000 to configure matching network circuit 250 usingbuilt-in solid-state electronic switches such as thyristors and IGBTs toselect, for example, one of several tuning capacitors and connect it inseries and/or in parallel to a combination of a fixed inductor and afixed load capacitor. The three passive elements then form an outputmatching network using a specific combination of C_(T), C_(L), and Laligned with the respective operating frequency band.

Although the passive component (e.g., a tuning capacitor) correspondingto the RF frequency specified in the process recipe 120 may be selected,it may still not be sufficient for adequate impedance matching betweenthe broadband RF power amplifier 1000 and the load impedance connectedat the output port O, such as the impedance of the plasma processingapparatus 111 in FIG. 1. The impedance of the output matching networkmay have to be adjusted further because the load impedance comprises notonly the impedance of the hardware (e.g., the RF electrode and cables)but also the impedance of the plasma that may be variable, even duringthe same process step. Sub-optimal impedance matching degrades the powertransfer efficiency and is indicated by a larger reflected power fromthe output port O normalized to the forward power dissipated in theload.

Embodiments in this disclosure may rapidly minimize the normalizedreflected power by continually adjusting the impedance of the selectedoutput matching network using a feedback control system that continuallyfine-tunes the frequency of RF signal with continual adjustments made tothe first control signal transmitted to the RF signal generator 100. Invarious embodiments, output power from the array of power amplifiers 220may also be changed while fine tuning the frequency for minimalreflected power. Several methods of generating an appropriate feedbacksignal that may be used to optimize the impedance matching are describedfurther below.

Still referring to FIG. 2, in one embodiment, the reflected power andforward power are measured by a power analyzer circuit 260. The outputof the output matching network circuit 250 is input to an incident portof the power analyzer circuit 260. The incident power mostly passesthrough the power analyzer circuit 260 to the output port O of thebroadband RF power amplifier 1000.

In one or more embodiments, the reflected power and forward power may bemeasured by using a broadband RF V-I sensor that independently sensesthe magnitudes and phases of the voltage (V) and current (I) of the RFsignal that exits the power analyzer circuit 260. Circuitry internal tothe power analyzer circuit 260 may analyze the measured V and I togenerate a feedback signal proportional to the normalized reflectedpower (indicated as R in FIG. 2) at the feedback port Z.

In some embodiments, a V-I sensor is used to measure the reflected powerand forward power, as described above, while in some other embodiments,a directional coupler may be used to directly detect the forward andreflected power. The output of the output matching network circuit 250may be input to an incident port of the directional coupler placedwithin the power analyzer circuit 260. The through port of thedirectional coupler may be connected to the output port O. A known smallfraction of the forward RF signal appears at the coupled port and thereflected RF signal appears at the isolated port of the directionalcoupler. Other circuitry in the power analyzer circuit 260 may generatethe feedback signal (R) proportional to the normalized reflected powerat the feedback port Z.

The broadband plasma processing system 1111 described in this disclosurecomprises the broadband RF power amplifier 1000 with several built-incircuits, such as the matching network circuit 250 and the poweranalyzer circuit 260. However, it is understood that, in some otherembodiment, components that are integrated in the broadband RF poweramplifier 1000 may be relocated outside, and components outside thebroadband RF power amplifier 1000 may be integrated without altering thefunctionality of the broadband plasma processing system 1111. Forexample, the matching network circuit 250 or the power analyzer circuit260 may be integrated in a separate component from the broadband RFpower amplifier 1000. Similarly, in another illustration, the RF signalgenerator 100 may be integrated within the broadband RF power amplifier1000.

As shown in FIG. 1, the feedback signal from the feedback port Z is sentto the programmable controller 11 o. The programmable controller 110continuously processes the feedback signal from the feedback port Z andrefines the first control signal to adjust the frequency of the tunableRF signal generator 100 within a narrow band centered at the frequencyspecified in the process recipe. This feedback method of continuallyfine-tuning the RF frequency till the impedance is matched for maximumpower transfer efficiency from the broadband RF power amplifier 1000 tothe first RF electrode 156 and the plasma is referred to as frequencysweep tuning with center frequency offset, and may be used for ultrafastimpedance matching.

FIG. 3 shows a schematic representation of a broadband plasma processingsystem 3333, wherein the RF signal power for sustaining the plasma isgenerated and controlled using the same method as described for thebroadband plasma processing system 1111 illustrated schematically inFIG. 1. However, in this embodiment, the plasma processing apparatus 333comprises a plasma processing chamber 350, where the substrate holder158 is used as a first RF electrode. In particular, there is no separatefirst RF electrode 156 (or top electrode), as in the embodimentillustrated in FIG. 1. As illustrated in FIG. 3, instead of connectingthe substrate holder 158 to ground, the substrate holder 158 of theplasma processing apparatus 333 is connected to the output port O of thebroadband RF power amplifier 1000, and the RF power is used to sustain adirect plasma in close proximity to the substrate (not shown). Thebroadband RF power amplifier 1000 of FIG. 3 may be similar to thebroadband RF power amplifier 1000 described using FIG. 2.

In various embodiments, the broadband plasma processing systems 1111 and3333 may operate the respective plasma processing apparatus 111/333between a first frequency band and a second frequency band sequentiallyor alternately. In a sequential operation mode, the substrate undergoesat least two sequential plasma process steps before exiting the plasmaprocessing chamber 150/350. A first plasma process step (e.g., a PECVDprocess) is first performed using RF power at the first frequency, andis followed by a second plasma process step (e.g., an RIE process step)performed using RF power at the second frequency.

In the alternating operation mode, a cyclic plasma process step (e.g., aBosch etch process) may be performed by alternating between plasmaetching and plasma deposition using, for example, the first frequencyduring the plasma deposition and the second frequency during the plasmaetch.

In order to provide RF power at multiple frequencies to the first RFelectrode 156 (for the plasma processing apparatus 111) or the substrateholder 158 (for the plasma processing apparatus 333), the process recipe120 may include explicit instructions for the programmable controller110 to configure the output matching network of the broadband RF poweramplifier 1000 and the tunable RF signal generator 100 to switch betweentwo frequency bands synchronously by using the pair of first and secondcontrol signals, as discussed above. Alternatively, the programmablecontroller 110 may by itself determine the different configurations forthe output matching network circuit 250 and/or input for the tunable RFsignal generator 100, based on the operating frequency defined by theprocess recipe 120.

Although the sequential operation mode and the alternating operationmode are described herein with reference to a first frequency and asecond frequency, it is understood that the embodiments disclosed inthis application can be used to accommodate more than two frequencies.

FIG. 4 illustrates a broadband plasma processing system 4444, whereinthe designs of the plasma processing apparatus 11 and 333, describedabove with reference to FIGS. 1 through 3, are combined to enhance theflexibility in adjusting the properties of plasma discharge in theplasma processing chamber 450. The RF signal power for sustaining theplasma is generated and controlled using the same method as describedfor the broadband plasma processing systems 1111 and 3333. The broadbandRF power amplifier 1000 of FIG. 4 may be similar to the broadband RFpower amplifier 1000 described using FIG. 2.

As illustrated in FIG. 4, the plasma processing apparatus 444 uses twoRF electrodes: a first RF electrode 156 located near the top of theplasma processing chamber 450 and a second RF electrode which is thesubstrate holder 158 near the base 105. Both the first RF electrode 156and the substrate holder 158 receive power from the output port O of thebroadband RF power amplifier 1000.

However, in this embodiment, the signal to the first RF electrode 156 isfiltered by a first bandpass filter 440 that blocks RF power outside afirst frequency band and the signal to the substrate holder 158 isfiltered by a second bandpass filter 455 that blocks RF power outside asecond frequency band. By inserting the first and second bandpassfilters 440 and 455 in the respective signal paths, the broadband plasmaprocessing system 4444 provides a method to perform sequential andalternating plasma processes on a semiconductor substrate. Thus, thefirst RF electrode 156 may be powered at the same time as the substrateholder 158 or they may be alternatively powered. However, the firstbandpass filter 440 ensures that the first RF electrode 156 is poweredat the first frequency band while the substrate holder 158 is powered atthe second frequency band.

The broadband plasma processing system 4444 may additionally include twoindependent DC power supplies, one used to superimpose a first DC biasV1 on the first RF electrode 156 and the other used to superimpose asecond DC bias V2 on the substrate holder 158 (the second RF electrode).The first and second DC bias values may be controlled by theprogrammable controller 110 or disabled, in accordance with the processrecipe 120 of the broadband plasma processing system 4444.

FIG. 5 illustrates an example of a dual-frequency broadband plasmaprocessing system 5555 comprising the plasma processing apparatus 444having two RF electrodes (described with reference to FIG. 4). The twoRF electrodes may be simultaneously powered by independent RF signals attwo discrete frequencies during dual-frequency operation.

As mentioned above, it is understood that the choice of dual-frequencyin this embodiment and prior embodiments is for illustration only; thevarious plasma systems discussed in this application such as thedual-frequency broadband plasma processing system 5555 can be used toaccommodate more than two frequencies.

As illustrated in FIG. 5, RF power from two isolated output ports O₁ andO₂ of a dual channel broadband RF power amplifier 5000 of thedual-frequency broadband plasma processing system 5555 may be used toindependently power the first RF electrode 156 and the substrate holder158 (the second RF electrode). Two independent RF signals, generated bya tunable dual channel RF signal generator 500, drives input ports I₁and I₂ of the dual channel broadband RF power amplifier 5000, asillustrated in FIG. 5.

The frequency bands of the two RF input signals are synchronouslycontrolled with a first control signal sent to the tunable dual channelRF signal generator 500 from a dual channel programmable controller 510.The dual channel programmable controller 510 also sends two controlsignals to the signal ports S₁ and S₂ of the dual channel broadband RFpower amplifier 5000 to synchronize the frequency bands to therespective output matching networks in the dual channel broadband RFpower amplifier 5000. The control signals used to select the frequencybands and configure the output matching networks synchronously are inaccordance with a process recipe 520 of the dual-frequency broadbandplasma processing system 5555.

Feedback signals from two impedance ports Z₁ and Z₂ of the dual channelbroadband RF power amplifier 5000 are used to fine tune the frequencies.As in the prior embodiments, the feedback signals may be used to adjustthe impedance of the output matching networks for the most efficientpower transfer during plasma processing and the input to the dualchannel RF signal generator 500.

As in the prior embodiment, the dual-frequency broadband plasmaprocessing system 5555 may additionally include two independent DC powersupplies for applying a first DC bias V1 and a second DV bias V2 to thefirst RF electrode 156 and the substrate holder 158. The applied DC biasvoltages may be controlled by the dual channel programmable controller510, as described above for the broadband plasma processing system 4444.

The dual channel broadband RF power amplifier 5000, used in thedual-frequency broadband plasma processing system 5555 in FIG. 5, isillustrated in further detail in FIG. 6. As indicated schematically bythe two dashed rectangles in FIG. 6, each channel of the eight-port dualchannel broadband RF power amplifier 5000 is a four-port single channelbroadband RF power amplifier, similar to the single channel broadband RFpower amplifier 1000 illustrated in FIG. 2. Thus, the dual channelbroadband RF power amplifier 5000 may include two of the single channelRF power amplifier described in prior embodiments such as FIG. 2.Accordingly, the operation of the dual channel broadband RF poweramplifier 5000 may be similar except that due to more number ofcomponents, separate channels can be processed in parallel tosimultaneously produce a dual-frequency output at output ports O1 andO2.

FIGS. 7 and 8 illustrate two examples of broadband plasma processingsystems 7777 and 8888 suitable for pulsed sequential or alternatingplasma processing. Pulsed plasma processing differs from continuousplasma processing in that RF power to the plasma discharge is choppedinto short pulses (e.g., 10 millisecond pulses) using, for example, aprogrammable chopper circuit comprising electronic switching devices andpulse generator circuitry. The plasma processing system is otherwise thesame as the respective system used for continuous plasma processing.

As illustrated in FIGS. 7 and 8, the broadband plasma processing systems7777 and 8888 have a chopper circuit 700 inserted in the signal pathconnecting the output of the tunable RF signal generator 100 to theinput port I of the broadband RF power amplifier 1000 of the broadbandplasma processing systems 1111 and 4444, respectively. The choppercircuit 700 may be controlled by a programmable controller 710.

Except for the chopper circuit 700 and the control path from theprogrammable controller 710, the schematic view of broadband plasmaprocessing system 7777 in FIG. 7 is same as that of the broadband plasmaprocessing system 1111 in FIG. 1. Likewise, the schematic view ofbroadband plasma processing system 8888 in FIG. 8 is same as that of thebroadband plasma processing system 4444 in FIG. 4 except for the choppercircuit 700 and the corresponding control path. Although not shown, thechopper circuit 700 may be added similarly to the embodiment describedin FIG. 3.

The chopper circuit of the chopper circuit 700 interrupts/modulates thecontinuous RF signal by periodic opening and closing of electronicswitches controlled by a low frequency pulse generator in the choppercircuit 700. The frequencies of the low frequency pulse waveform are ofthe order of 100 Hz, whereas the frequencies of the RF signal from thetunable RF signal generator 100 are between about 100 kHz to about 10GHz. The chopper circuit 700 may be triggered and the frequency and dutycycle of the low frequency pulses used to modulate the RF signal fromthe tunable RF signal generator 100 may be controlled by theprogrammable controller 710 with a control signal sent to a controlterminal P of the chopper circuit 700, as illustrated in FIGS. 7 and 8.

In some pulsed processing applications, the RF signal may be switchedoff during certain pulses during which no plasma processing isperformed. For example, PEALD and PEALE utilize alternating reaction andpurge pulses during one reaction cycle. Accordingly, the RF signalgenerator 100 is toggled on (reaction pulse) and off (purge pulse) bythe programmable controller 710. The instantaneous RF power waveform atthe output port O of the broadband RF power amplifier 1000 could exhibittransient variations for a brief time after the plasma discharge isinitiated at the start of a reaction pulse. The transient may be aresult of the impedance mismatch caused by the plasma component of theload impedance changing rapidly with time as the plasma is ignited whenRF power is turned on. The ultrafast impedance matching (e.g., aresponse time of less than 100 microsecond) using the frequency sweeptuning with center frequency offset, as described above for thebroadband plasma processing systems 1111 and 3333, provides theadvantage of reducing transients in RF power supplied to the plasmaprocessing apparatus 444 during pulsed plasma processing. Precisecontrol of RF power supplied to the plasma during each pulse of a pulsedplasma process step may be achieved by reducing (or even eliminating)the uncontrolled transient variations.

FIG. 9 illustrates an alternative embodiment of a broadband plasmaprocessing systems 9999 suitable for pulsed sequential or alternatingplasma processing. This embodiment is similar to the prior embodimentsof FIGS. 7-8 to include a chopper circuit that may interrupt/modulatecontinuous RF signals. However, unlike the embodiment described in FIG.5, the example embodiment in FIG. 9 may include a dual channel choppercircuit 900 in the signal paths between a tunable dual channel RF signalgenerator 500 and a dual channel broadband RF power amplifier 5000. Thedual channel chopper circuit 900 may include multiple units of thechopper circuit 700 described in prior embodiments and may receivemultiple pulse control signals at its control terminals P1 and P2 fromthe dual channel programmable controller 910 (which operates similar tothe previously discussed dual channel programmable controller 510besides also providing the control signals for the dual channel choppercircuit 900).

FIG. 10 discloses a method of operating a plasma processing system inaccordance with an embodiment of the present invention. The method ofFIG. 10 may be applied to any of the systems described in FIGS. 1-9.

Referring to FIG. 10, at a tunable RF signal generator (e.g., tunable RFsignal generator 100 of FIG. 1), a radio frequency (RF) signal isgenerated (box 21).

At a broadband RF power amplifier (e.g., at broadband RF power amplifier1000 of FIG. 1), the RF signal is amplified to generate an amplified RFsignal (box 22). This amplified RF signal is supplied to an RF electrode(e.g., first RF electrode 156 of FIG. 1) to power a plasma within aplasma processing chamber (box 23). A feedback signal is generated at,e.g., the broadband RF power amplifier 1000 that incorporates ameasurement of a reflected power at the output of the broadband poweramplifier (box 24). The reflected power includes the effect of theimpedance of the plasma and is measured using a broadband V-I sensor ora directional coupler. The frequency of the RF signal is adjusted at,e.g., tunable RF signal generator 100, based on the feedback signal.

In an illustrative embodiment (see FIG. 1 as representative system), adeposition process step may be performed first. At the depositionprocess step, the tunable RF signal generator 100 sends a signal at thefirst frequency (e.g. a high RF frequency (f1)) at desired amplitude tothe broadband RF power amplifier 1000, which amplifies the power andoutputs it to the first electrode 156 to ignite a high density firstplasma. As soon as the first plasma is ignited, the tunable RF signalgenerator 100 starts a frequency sweep around the high RF frequency f1with a certain offset range Δf1 to minimize the reflected power beingmeasured by the power analyzer circuit 260 within the broadband RF poweramplifier 1000. The deposition step will begin, and deposition cancontinue for several reaction cycles (sequential reaction and purgepulses) as in plasma enhanced atomic layer deposition (PEALD).

Next, an exemplary etch process step may be initiated. At the etch step,the tunable RF signal generator 100 switches output frequency and sendsa signal at the second frequency (e.g. a low RF frequency f2) at adesired amplitude to the broadband RF power amplifier 1000. For example,in one illustration, the high RF frequency f1 is at least 1.1 times thelow RF frequency f2. For example, an embodiment may use a low RFfrequency of 27 MHz and a high RF frequency of 40 MHz while anotherembodiment may use a low RF frequency of 40 MHz and a high RF frequencyof 60 MHz. Alternately, in other examples, the high RF frequency f1 isat least two times the low RF frequency f2. The broadband RF poweramplifier 1000 amplifies the received signal at the second frequency andoutputs it to the first electrode 156 to ignite a second plasma. As soonas the second plasma is ignited, the tunable RF signal generator 100starts a frequency sweep around the low frequency f2 with a certainoffset range Δf2 to minimize the reflected power being measured by thepower analyzer circuit 260 within the broadband RF power amplifier 1000.This starts the etching of the material, e.g., a substrate on substrateholder 158 in the plasma processing chamber. Additional method stepsespecially those particular to a particular hardware design arediscussed in more detail above (FIGS. 1-9) while discussing thosefeatures and are not repeated herein for brevity.

Accordingly, in various embodiments, the process can quickly togglebetween etching and deposition by changing the frequency at the tunableRF signal generator 100 without having to use mechanically driventuning, as done in conventional equipment.

Accordingly, embodiments of the present application disclose broadbandplasma systems and methods for operating a plasma processing apparatusin a sequential, alternating, or pulsed mode.

Accordingly, various embodiments of this invention can achieve fast andsmooth transitions of RF power between discrete power levels (e.g.,between on and off) or between discrete RF frequencies (e.g., between 10MHz and 100 MHz), as programmed in a plasma process recipe. In addition,fine tuning of the RF frequency within a narrow band can be achieved byusing a programmable controller in a feedback control system. Thefeedback control system comprises an externally tunable broadband RFsignal generator connected to a broadband RF power amplifier fitted withan electronically configurable output matching network, and may beconfigured by the programmable electronic controller. The fine frequencytuning can be used to rapidly adjust the frequency-dependent impedanceof the matching network to match the impedance of the plasma processingapparatus (including the impedance of the plasma) with the outputimpedance of the broadband RF power amplifier to achieve efficient powertransfer. As described in further detail above, the electroniccontroller dynamically tunes the output frequency of the RF signalgenerator using feedback of the plasma processing apparatus impedancemeasured using, for example, an RF voltage-current (V-I) sensorintegrated into the output stage of the broadband RF power amplifier.

Example embodiments of the invention are summarized here. Otherembodiments can also be understood from the entirety of thespecification as well as the claims filed herein.

Example 1

A plasma processing system includes a plasma processing chamber, a firstelectrode for powering a plasma in the plasma processing chamber, atunable radio frequency (RF) signal generator configured to output afirst signal at a first frequency and a second signal at a secondfrequency. The second frequency is at least 1.1 times the firstfrequency. The system further includes a broadband power amplifiercoupled to the tunable RF signal generator, the first frequency and thesecond frequency being within an operating frequency range of thebroadband power amplifier. The output of the broadband power amplifieris coupled to the first electrode. The broadband power amplifier isconfigured to supply, at the output, first power at the first frequencyand second power at the second frequency.

Example 2

The plasma processing system of example 1, where the broadband poweramplifier is configured to supply simultaneously, at the output, thefirst power and the second power.

Example 3

The plasma processing system of example 1, where the broadband poweramplifier is configured to supply sequentially, at the output, the firstpower and the second power.

Example 4

The plasma processing system of one of examples 1 to 3, furtherincluding: a second electrode disposed in the plasma processing chamber,the second electrode being coupled to the output of the broadband poweramplifier.

Example 5

The plasma processing system of one of examples 1 to 4, furtherincluding: a first bandpass filter disposed between the output of thebroadband power amplifier and the first electrode, the first bandpassfilter having a first passband to pass through the first frequency andfilter the second frequency; and a second bandpass filter disposedbetween the output of the broadband power amplifier and the secondelectrode, the second bandpass filter having a second passband to passthrough the second frequency and filter the first frequency.

Example 6

The plasma processing system of one of examples 1 to 5, furtherincluding: a chopper circuit disposed between the tunable RF signalgenerator and the broadband power amplifier, the chopper circuitconfigured to modulate the first signal and the second signal with alower frequency pulse signal.

Example 7

The plasma processing system of one of examples 1 to 6, where thechopper circuit includes: a low frequency pulse generator; andelectronic switches disposed in a signal path between the tunable RFsignal generator and the broadband power amplifier, the electronicswitches being controlled by the low frequency pulse generator.

Example 8

The plasma processing system of one of examples 1 to 7, where the outputof the broadband power amplifier includes a first output port to outputthe first power at the first frequency and a second output port tooutput the second power at the second frequency.

Example 9

The plasma processing system of one of examples 1 to 7, where the outputof the broadband power amplifier includes a single output port to outputthe first power at the first frequency and the second power at thesecond frequency.

Example 10

A plasma processing system includes a tunable radio frequency (RF)signal generator configured to output a first signal at a firstfrequency and a second signal at a second frequency. The secondfrequency is at least 1.1 times the first frequency. The system furtherincludes a broadband power amplifier coupled to the tunable RF signalgenerator. The first frequency and the second frequency is within anoperating frequency range of the broadband power amplifier. The outputof the broadband power amplifier is configured to be coupled to anelectrode of a plasma processing chamber. The broadband power amplifieris configured to supply, at the output, first power at the firstfrequency and second power at the second frequency, and provide afeedback to tune the output of the broadband power amplifier to thefirst frequency or the second frequency.

Example 11

The plasma processing system of example 10, where the broadband poweramplifier includes: a plurality of power amplifiers coupled to an inputof the broadband power amplifier; a combiner coupled to an output of theplurality of power amplifiers; a directional coupler coupled to anoutput of the combiner and having an output coupled to the output of thebroadband power amplifier; and an impedance power analyzer circuitcoupled to the directional coupler or a V-I sensor and configured toprovide a feedback signal.

Example 12

The plasma processing system of one of examples 10 or 11, furtherincluding: an output matching network circuit coupled between the outputof the combiner and the directional coupler or a V-I sensor, the outputmatching network circuit including electronically configurable networkof passive elements.

Example 13

The plasma processing system of one of examples 10 to 12, furtherincluding: a programmable controller; a first signal path coupling theprogrammable controller to the tunable RF signal generator; a secondsignal path coupling the programmable controller to the output matchingnetwork circuit; and a third signal path coupling the impedance poweranalyzer circuit to the programmable controller.

Example 14

The plasma processing system of one of examples 10 to 13, where theprogrammable controller is configured to: receive the feedback signalfrom the impedance power analyzer circuit through the third signal path;provide a first control signal to the tunable RF signal generatorthrough the first signal path; and provide a second control signal tothe output matching network circuit.

Example 15

The plasma processing system of one of examples 10 to 14, where theoutput matching network circuit is configured to reconfigure the outputmatching network circuit based on the second control signal.

Example 16

A method of operating a plasma processing system comprises generating aradio frequency (RF) signal at tunable RF signal generator; at abroadband power amplifier, amplifying the RF signal to generate anamplified RF signal; supplying the amplified RF signal to power a plasmawithin a plasma processing chamber; generating a feedback signal bymeasuring an impedance of the plasma; and adjusting a frequency of theRF signal at the tunable RF signal generator based on the feedbacksignal.

Example 17

The method of example 16, further including reconfiguring an outputmatching network circuit based on the feedback signal.

Example 18

The method of one of examples 16 or 17, further including: supplying theamplified RF signal includes supplying the amplified RF signal to a topelectrode within the plasma processing chamber.

Example 19

The method of one of examples 16 or 17, further including: supplying theamplified RF signal includes supplying the amplified RF signal to asubstrate holder within the plasma processing chamber.

Example 20

The method of one of examples 16 to 19, further including: supplying theamplified RF signal includes supplying the amplified RF signal to afirst bandpass filter; outputting the amplified RF signal through thefirst bandpass filter when the amplified RF signal has a frequencywithin a first frequency range; coupling the output of the firstbandpass filter to a top electrode within the plasma processing chamber;supplying the amplified RF signal includes supplying the amplified RFsignal to a second bandpass filter; outputting the amplified RF signalthrough the second bandpass filter when the amplified RF signal has afrequency within a second frequency range; and coupling the output ofthe second bandpass filter to a substrate holder within the plasmaprocessing chamber.

Example 21

The method of one of examples 16 to 20, further including modulating theamplified RF signal with a lower frequency pulse signal, where supplyingthe amplified RF signal to power the plasma includes supplying themodulated amplified RF signal to power the plasma.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A method of operating a plasma processing system,the method comprising: generating a radio frequency (RF) signal attunable RF signal generator; at a broadband power amplifier, amplifyingthe RF signal to generate an amplified RF signal; supplying theamplified RF signal to power a plasma within a plasma processingchamber; generating a feedback signal by measuring an impedance of theplasma; and adjusting a frequency of the RF signal at the tunable RFsignal generator based on the feedback signal.
 2. The method of claim 1,further comprising reconfiguring an output matching network circuitbased on the feedback signal.
 3. The method of claim 1, furthercomprising: supplying the amplified RF signal comprises supplying theamplified RF signal to a top electrode within the plasma processingchamber or to a substrate holder within the plasma processing chamber.4. The method of claim 1, further comprising: supplying the amplified RFsignal comprises supplying the amplified RF signal to a first bandpassfilter; outputting the amplified RF signal through the first bandpassfilter when the amplified RF signal has a frequency within a firstfrequency range; coupling the output of the first bandpass filter to atop electrode within the plasma processing chamber; supplying theamplified RF signal comprises supplying the amplified RF signal to asecond bandpass filter; outputting the amplified RF signal through thesecond bandpass filter when the amplified RF signal has a frequencywithin a second frequency range; and coupling the output of the secondbandpass filter to a substrate holder within the plasma processingchamber.
 5. The method of claim 1, further comprising modulating theamplified RF signal with a lower frequency pulse signal, whereinsupplying the amplified RF signal to power the plasma comprisessupplying the modulated amplified RF signal to power the plasma.
 6. Themethod of claim 1, further comprising modulating, by a chopper circuit,the RF signal with a lower frequency pulse signal, the chopper circuitarranged between the tunable RF signal generator and the broadband poweramplifier.
 7. The method of claim 1, wherein the RF signal is a first RFsignal at a first frequency, the method further comprising generating,at the tunable RF signal generator, a second RF signal at a secondfrequency, the second frequency being at least 1.1 times the firstfrequency.
 8. A method of operating a plasma processing system,comprising: generating, by a radio frequency (RF) signal generator, afirst signal at a first frequency and a second signal at a secondfrequency; amplifying, by an amplifier circuit, the first signal and thesecond signal, the amplifier circuit having an output coupled to anelectrode of a plasma processing chamber; generating, by a sensor of theamplifier circuit, a feedback signal based on a reflection of the firstsignal and the second signal at the output of the amplifier circuit;generating, by a controller, a control signal based on the feedbacksignal; and configuring a matching network circuit based on the controlsignal received from the controller to provide a matching networkconfiguration at the output of the amplifier circuit, the matchingnetwork circuit arranged between the RF signal generator and the sensor.9. The method of claim 8, further comprising modulating, by a choppercircuit, the first signal and the second signal with a lower frequencypulse signal, the chopper circuit arranged between the RF signalgenerator and the amplifier circuit.
 10. The method of claim 9, whereinthe chopper circuit comprises: a low frequency pulse generator; andelectronic switches disposed in a signal path between the RF signalgenerator and the amplifier circuit, the electronic switches beingcontrolled by the low frequency pulse generator.
 11. The method of claim10, further comprising measuring the reflection of the first signal andthe second signal at the output of the amplifier circuit.
 12. The methodof claim 8, wherein the amplifier circuit comprises a plurality ofamplifiers and a combiner, wherein amplifying the first signal and thesecond signal comprises: distributing the first signal and the secondsignal to each of the plurality of amplifiers; amplifying by eachamplifier the first signal and the second signal to generate arespective amplified signal; and combining, by a combiner of theamplifier circuit, an amplified coupled to an output of the RF signalgenerator, each amplifier configured to amplify each of the respectiveamplified signals and generate an amplified first signal and anamplified second signal.
 13. The method of claim 12, further comprisingsimultaneously supplying, at the output of the amplifier circuit, theamplified first signal and the amplified second signal.
 14. The methodof claim 8, wherein the second frequency is at least 1.1 times the firstfrequency.
 15. A method of operating a plasma processing system,comprising: outputting, by a tunable radio frequency (RF) signalgenerator, a first signal at a first frequency and a second signal at asecond frequency, the second frequency being at least 1.1 times thefirst frequency; supplying, at an output of a broadband power amplifier,first power at the first frequency and second power at the secondfrequency, the broadband power amplifier coupled to the tunable RFsignal generator, the first frequency and the second frequency beingwithin an operating frequency range of the broadband power amplifier,and an output of the broadband power amplifier coupled to an electrodeof a plasma processing chamber; and generating a feedback signal to tunethe output of the broadband power amplifier to the first frequency orthe second frequency.
 16. The method of claim 15, wherein the broadbandpower amplifier comprises: a plurality of power amplifiers coupled to aninput of the broadband power amplifier; a combiner coupled to an outputof the plurality of power amplifiers; a directional coupler coupled toan output of the combiner and having an output coupled to the output ofthe broadband power amplifier; and an impedance power analyzer circuitcoupled to the directional coupler or a V-I sensor.
 17. The method ofclaim 16, further comprising generating, by the impedance power analyzercircuit, a feedback signal based on a reflection of the first signal andthe second signal at the output of the output of the broadband poweramplifier.
 18. The method of claim 17, further comprising generating, bya controller, a control signal based on the feedback signal.
 19. Themethod of claim 18 further comprising reconfiguring electronicallyconfigurable network of passive elements of an output matching networkcircuit based on the control signal, and the output matching networkcircuit coupled between the output of the combiner and the directionalcoupler or a V-I sensor.
 20. The method of claim 15, further comprisingmodulating, by a chopper circuit, the first signal and the second signalwith a lower frequency pulse signal, the chopper circuit arrangedbetween the tunable RF signal generator and the broadband poweramplifier.